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Generation, Transmission and Distribution, IEE Proceedings-

Issue 6 • Date Nov 1994

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Displaying Results 1 - 16 of 16
  • Fast identification of symmetrical components by use of a state observer

    Publication Year: 1994 , Page(s): 617 - 622
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    The paper presents the synthesis of a state observer which can be applied to estimation of the current and voltage symmetrical components in a three-phase electrical network. The state observer algorithm is based on the recursive model of the current and voltage generation process in a three-phase power system in which the orthogonal phasors are used as the model state variables. The synthesis of the state observer is shown under the assumption that the higher harmonics as well as the decaying DC offset may be present in the symmetrical component phasors. The state observer presented can be used as the fast current and voltage symmetrical component estimator in digital power protection systems. The calculation example included shows the basic properties of the observer in such an application View full abstract»

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  • New technique of network partitioning for voltage collapse margin calculations

    Publication Year: 1994 , Page(s): 630 - 636
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    Voltage collapse is associated with a stress condition of power systems. Control actions must provide the desired results, otherwise a system may operate in an unknown condition. It has been shown that this unknown condition is associated with two regions of operation and the boundary between them. The boundary between the two regions is related to a singular load-flow Jacobian. To identify the critical bus, a reduction of the load-flow Jacobian in relation to each load bus is developed. To reduce the computational burden associated with large power networks, a network partitioning is proposed which is based on voltage variation at each load bus in relation to load variation at the other load busses. Comparison between the proposed method and network partitioning using Sanchis' method is presented. The weak area of a power system is identified in the network partitioning; a weak area is defined as the area that contains the critical bus of the power network. To calculate the margins for each load bus of the weak area, the relation between load variation at each load bus and voltage magnitude and phase angle variations at the critical bus is normalised, one by one. The busses strongly connected to the critical bus have smaller load variation in relation to the busses weakly connected to the critical bus. The proposed method has been tested using the IEEE 24-bus and 300-bus systems View full abstract»

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  • Forecasting daily load curves using a hybrid fuzzy-neural approach

    Publication Year: 1994 , Page(s): 561 - 567
    Cited by:  Papers (22)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    A new approach to electric load forecasting which combines the powers of neural network and fuzzy logic techniques is proposed. Expert knowledge represented by fuzzy rules is used for preprocessing input data fed to a neural network. For training the neural network for one-day ahead load forecasting, fuzzy if-then rules such as `If x1 is high and x2 is low, then y is positive small' are used, in addition to historical load and weather data that are usually employed in conventional supervised learning methods. The fuzzy front-end processor maps both fuzzy and numerical input data to a fuzzy output. The input vector to the neural network consists of these membership values to linguistic properties. To deal with the linguistic values such as high, low, and medium, an architecture of neural network that can handle fuzzy input vectors is propounded. The proposed method effectively deals with trends and special events that occur annually. The fuzzy-neural network is trained on real data from a power system and evaluated for forecasting next-day load profiles based on forecast weather data and other parameters. Simulation results are presented to illustrate the performance and applicability of this approach. A comparison of results with other commonly used forecasting techniques establishes its superiority View full abstract»

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  • Tower modelling for lightning surge analysis using Electro-Magnetic Transients Program

    Publication Year: 1994 , Page(s): 637 - 639
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    For economical insulation co-ordination in transmission and substation equipment, it is necessary to accurately predict the lightning surge overvoltage that occurs in an electric power system. The lightning surge response of transmission towers is one of the main factors that influences the magnitude and the waveshape of the surge arriving at a substation. The paper presents a tower model, based on a finite-difference transmission-line model, that can be used with EMTP. Computation results obtained, for a typical double-circuit 500 kV tower, are in good agreement with field test measurements View full abstract»

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  • Fuzzy linear programming: an application to hydroelectric generation scheduling

    Publication Year: 1994 , Page(s): 568 - 574
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    A new approach using fuzzy linear programming is proposed for solving the hydroelectric generation scheduling problem. A characteristic feature of this approach is that the errors in the forecast hourly loads and natural inflows can be taken into account by using fuzzy set notation, making the approach superior to the conventional linear programming method in which the hourly loads and natural inflows are assumed to be exactly known and there are no errors in the forecast loads and natural inflows. To reach an optimal schedule under the uncertain environment, a fuzzy linear programming model in which the hourly loads, the hourly natural inflows and the cost are all expressed in fuzzy set notations is developed. The developed fuzzy linear programming approach is applied to schedule the generation in the Taiwan power system which contains ten hydroplants including cascaded ones. It is found that the proposed approach is very effective in obtaining proper hydrogeneration schedules in uncertain conditions View full abstract»

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  • Interactive fuzzy satisfying method for optimal multi-objective VAr planning in power systems

    Publication Year: 1994 , Page(s): 554 - 560
    Cited by:  Papers (10)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    The paper presents an interactive fuzzy satisfying method for solving a multi-objective VAr planning problem by assuming that the decision maker (DM) has imprecise or fuzzy goals for each of the objective functions. Through the interaction with the DM, the fuzzy goals of the DM are quantified by eliciting corresponding membership functions. If the DM specifies the reference membership values, the minimax problem is solved for generating a corresponding global noninferior optimal solution for the DM's reference membership values. Then, by considering the current values of the membership functions as well as the objectives, the DM acts on this solution by updating the reference membership values. The interactive procedure continues until the satisfying solution for the DM is obtained. The minimax problem can be easily handled by the simulated annealing (SA) approach which can find a global optimal solution even for the solution space which is nonconvex and the objective functions which are nondifferentiable. Results of the application of the proposed method are presented View full abstract»

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  • Application of clustering and factorisation tree techniques for parallel solution of sparse network equations

    Publication Year: 1994 , Page(s): 609 - 616
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    Through the use of diakoptical techniques it is possible to solve the network equations for a power system using a parallel computer architecture. Traditional parallel solution techniques give an unimpressive return on investment as more processors are applied to the problem owing to unacceptably large sequential sections of the algorithm and ill-balanced computational loads. The paper analyses the diakoptical method using the factorisation tree as a tool. New algorithms are proposed for network splitting, node ordering and load balancing between processors. This, in connection with a novel recursively parallel solution algorithm, gives improved speedup over the conventional parallel solution method. Simulation results are presented which confirm the usefulness of the method View full abstract»

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  • Power based algorithm to provide loss of grid protection for embedded generation

    Publication Year: 1994 , Page(s): 640 - 646
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The paper introduces a new protection algorithm designed to detect when the connection between an embedded generator operating and the utility grid is lost. Once loss of grid is detected the intertie circuit breaker connecting the embedded generator to the utility should be opened to allow the orderly restoration of supply to other utility consumers. Failure to detect the loss of grid and subsequently open the intertie breaker could result in utility consumers receiving a low quality supply and could expose the embedded generator to severe damage should the utility grid be reconnected while out of synchronism with the embedded generator. The paper describes the basis for the operation of the protection algorithm and the role of the various elements together with the derivation of the tripping criterion. Its response to a series of power system switching scenarios are presented, including loss of grid, independent operation, out-of-phase reclosure, parallel operation together with a selection of fault studies, and for each it is shown to operate as required View full abstract»

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  • Benefits of wheeling economy energy in Canada: quantification and sensitivity analysis

    Publication Year: 1994 , Page(s): 585 - 593
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    The paper describes the studies carried out by the National Energy Board to quantify potential wheeling benefits as part of its review of possible measures for enhancing transmission access in Canada. Computer simulations were performed on a planning time horizon to determine potential benefits from bilateral exchanges of economy energy and the additional benefits which could result from various wheeling arrangements. The simulations modelled the interconnected power systems of eastern Canada and the neighbouring American utilities which make up the Northeast Power Coordinating Council. From these simulations, the potential benefits for each system involved as well as the net potential benefits were determined. The CPU time for the simulations ranged from 14 h to 46 h on a VAX 8200 minicomputer. Sensitivity analyses were also performed to establish the sensitivity of the results to some operational assumptions and parameters used in the studies View full abstract»

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  • Power system network topology error detection

    Publication Year: 1994 , Page(s): 623 - 629
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    The accuracy of state estimation determines the usefulness of real-time power system operation and control applications. To have an accurate state estimation it is essential to have the capability of detecting bad measurement data and topology errors in the model. While analogue measurement errors have received considerable attention, relatively little effort has been given to detection of topology errors. A procedure that combines numerical computation and various consistency checks is proposed to detect topology errors in the state estimation model. Tests based on real-time measurement data collected in an energy control centre have indicated that the proposed method can be used to detect branch inclusion, exclusion and bus configuration errors View full abstract»

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  • Inclusion of weather effects in composite system reliability evaluation using sequential simulation

    Publication Year: 1994 , Page(s): 575 - 584
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (816 KB)  

    The studies reported in the paper describe the development of a new technique to accommodate the modelling of weather events in composite system reliability evaluation using a sequential simulation technique. Although considerable effort has been made to include weather impacts, all the available techniques neglect the moving or traversing nature of weather events. The technique described not only takes into account a comprehensive range of weather severities and attributes, it also accommodates the traversing nature of weather events. The sequential Monte Carlo simulation approach travels through time chronologically, and this unique concept allows it to be used for tracking the effects of nonstationary weather events within the evaluation procedure of transmission systems. Eventually this approach leads to an improved representation of a composite system. The approach is demonstrated by sensitivity studies conducted on the IEEE Reliability Test System. These results show the applicability of the algorithms for evaluating the reliability of a composite power system View full abstract»

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  • Block diagram transfer function model of a generator including damper windings

    Publication Year: 1994 , Page(s): 599 - 608
    Cited by:  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    A transfer function model of a system provides an excellent basis for the analysis, explanation and assessment of its dynamic behaviour and in the case of a turbogenerator, the model proposed by de Mello and Concordia (1969) has been extensively used for such purposes for many years. The paper presents an extended transfer function block diagram model of a generator based on a standard, widely used and accepted representation, which includes damper windings on both d and q axes and is capable of providing a much more reliable basis for analysis and performance assessment. Frequency response analysis is employed to demonstrate the relative capabilities of the model form and to explain fundamental dynamic characteristics View full abstract»

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  • Multivariable adaptive control of AC-DC systems

    Publication Year: 1994 , Page(s): 658 - 664
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    The conventional design of HVAC-DC system controllers is based on model linearisation at operating points, hence transient performance cannot be guaranteed. A minimum variance adaptive control scheme is developed for improving the generator performance and hence power system stability. The controller supplies the excitation system and both terminals of a DC link with control signals derived from a control strategy which minimises the variance between system outputs and outputs of a linear predictor. Results obtained from a detailed nonlinear simulation of a two-machine AC-DC system are presented View full abstract»

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  • Probability distribution approach to describe customer costs due to electric supply interruptions

    Publication Year: 1994 , Page(s): 594 - 598
    Cited by:  Papers (10)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    Considerable attention is being devoted to quantitative determination of electric power system reliability worth. A basic approach is to utilise customer interruption costs obtained from postal or in person surveys. The results obtained are transformed into customer damage functions which are applicable to individual customer classes and sectors. Standard customer damage functions utilise average customer costs for selected outage durations. The paper presents a new approach which provides a three-dimensional representation of the probability distributions associated with customer outage costs. The results are utilised in a basic generating capacity adequacy assessment analysis to calculate an interrupted energy assessment rate, which provides an overall average cost per kilowatt-hour of unsupplied energy. This cost value is considerably higher than the value obtained using a conventional customer damage function View full abstract»

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  • Enhanced Newton-Raphson algorithm for normal, controlled and optimal powerflow solutions using column exchange techniques

    Publication Year: 1994 , Page(s): 647 - 657
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (788 KB)  

    A column exchange approach for powerflow (PF) problems is presented, in which various functional Jacobian matrices are obtained from a new basic formulation. Transformations between these matrices are described, which allow simple and flexible algorithms to be programmed. An enhanced version of the partitioned Newton-Raphson algorithm for normal, controlled and optimal PF yielded by the new approach is also presented. The new approach is shown to be much more powerful than the standard method. In addition to the calculation of normal PF solutions, the new algorithm can conveniently and efficiently model simple control activities, such as generator VAr limits, load-tap-changing transformers and variable phase shifting transformers. Complex control activities, such as control of remote variables or nonstandard system controls, as well as the calculation of sensitivity vectors for both objective functions and system constraints in optimal PF (OFF) can also be handled efficiently. Even when generator VAr limits, LTC transformers and transformer tap limits are included, the new algorithm still exhibits quadratic convergence. Computational efficiency is much greater than the traditional Newton-Raphson implementation (about seven times faster for practical UK systems) and is comparable with the fast decoupled loadflow (FDLF). The algorithm is also very reliable for systems with either meshed or radial configurations, including ill-conditioned networks View full abstract»

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  • Transient stability evaluation of multimachine power systems: a probabilistic approach based upon the extended equal area criterion

    Publication Year: 1994 , Page(s): 545 - 553
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (692 KB)  

    The probabilistic aspects of transient stability evaluation of electrical power systems are discussed. The stability properties of the system after a given fault are characterised by means of the instability probability, which is defined in terms of the critical clearing time and the fault clearing time. Particular attention is devoted to the probabilistic description of the load demand, characterised by a random vector, and its effect on the critical clearing time. The instability probability is evaluated by using an analytical approach, already proved satisfactory in the single-machine case, as shown in a previous paper by the authors. The method is illustrated with reference to a simple system: the critical clearing time is calculated, for each value of the random inputs, by means of the extended equal area criterion. Its probability distribution is then evaluated, by means of a regression technique, in terms of the load demand distribution. Such distribution is then used to calculate the instability probability as a function of the basic statistical parameters of the system. The proposed method allows a straightforward analytical determination of the influence of the system parameters on the instability probability. A peculiar aspect regarding a multinode system, which is also analysed in the paper, is the effect of the statistical correlation among the loads on the stability View full abstract»

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